Because of their high-water content, mouthwashes are challenging to preserve. Previous patents or patent applications have postulated that the hydrophilic phases of dual phase mouthwashes prepared with CPC and sodium fluoride (NaF) are preserved by the presence of sodium benzoate, potassium sorbate and/or methylisothiazolinone (MIT). This invention finds that the removal of both a fluoride source and MIT from a mouthwash greatly compromises its preservation, and that the preservation is dependent on a number of factors, including: 1) the presence of CPC, 2) the presence of benzyl alcohol, 3) the nature of a flavor used in the mouthwash, 4) the type of acid used to adjust the pH of the mouthwash, with a monovalent acid (e.g., phosphoric acid and/or HCl) being preferred over a multivalent acid (e.g., citric acid), and 5) the interaction between preservatives and CPC.